The present invention relates to a pattern forming method using a charged particle beam process, and a charged particle beam processing system and, more specifically, to a pattern forming method using a charged particle beam process and suitable for preventing the corrosion of a workpiece by a reactive gas when minutely processing the workpiece by using a charged particle beam and the reactive gas, and improvements in a charged particle beam processing system.
A charged particle beam, such as a focused ion beam or an electron beam, can be focused in a beam of a very small diameter. Fine processing of wiring patterns of semiconductor devices, such as LSI circuit devices, for the correction of the wiring patterns of semiconductor devices and the analysis of defects in semiconductor devices can be achieved by using the energy of a charged particle beam. Since fine processing using a charged particle beam is a sputtering process in which atoms or groups of atoms of the materials of the workpiece are caused to sputter by the impingement of the charged particle beam on the surface of the workpiece, the processing speed of the fine processing is relatively low, the selectivity of the fine processing in terms of the material of the sample, i.e., a workpiece, is relatively low, and it is very difficult to stop processing at a desired layer in a workpiece of a laminated structure having a plurality of layers of different materials.
Active studies have been made in recent years on processing techniques using a reactive gas and a charged particle beam, such as a focused ion beam or an electron beam, in combination. These processing techniques activate a reactive gas by the energy of a charged particle beam to induce a chemical reaction. Therefore, these processing techniques enable the rapid etching of a workpiece, and is capable of stopping processing at a desired layer of a material in a laminated structure by selectively using a reactive gas suitable for processing the layers of different materials of the workpiece.
A technique relating to a processing system using such a processing method is disclosed in JP-A No. 1-169860.
Although a pattern forming method (process) using, in combination, a reactive gas and a charged particle beam is capable of rapid processing, some reactive gases are highly corrosive to metals. For example, If chlorine gas (Cl2 gas) is employed as a reactive gas in processing a workpiece made of aluminum (Al), Cl2 gas adsorbed by the workpiece remains on the surface of the workpiece even if the supply of Cl2 gas is stopped. Therefore, the Cl2 gas retained on the surface of the workpiece by adsorption reacts with moisture contained in the atmosphere when the workpiece carrying the Cl2 gas is taken into the atmosphere, corrodes the Al workpiece and damages processed portions of the Al workpiece.
Nothing about the processing of the reactive gas adsorbed by the workpiece is considered by the prior art.
Accordingly, it is an object of the present invention to solve problems in the foregoing prior art and to provide a pattern forming method employing improved charged particle beam processing and a charged particle beam processing system capable of preventing the corrosion of a workpiece by a reactive gas retained on the surface thereof by adsorption when the workpiece is taken out from the processing chamber into the atmosphere.
The foregoing object can be achieved by a method (a) which forms a desired pattern in a processing chamber by etching a layer formed on a workpiece by a reactive process using, in combination, a reactive gas and a charged particle beam, and subjects the surface of the workpiece to a plasma sputter processing using a plasma of an inert gas before taking out the workpiece from the processing chamber into the atmosphere, a method (b) which heats a workpiece by a heating device, such as a heater or a lamp, a method (c) which coats the surface of a workpiece with a carbon film before subjecting the workpiece to a reactive pattern forming process, and removes the carbon film remaining on the surface of the workpiece by oxygen plasma ashing, a method (d) which forms a pattern by irradiating a workpiece with a charged particle beam while oxygen gas is blown against the surface of the workpiece in the atmosphere of a reactive gas or a method (e) which forms a pattern on a workpiece by irradiating the workpiece with both an oxygen beam and a charged particle beam.
The method (a) processes the workpiece by a plasma of an inert gas before taking out the workpiece from the processing chamber into the atmosphere by a plasma processing method which supplies an inert gas, such as Ar gas or N2 gas, at a flow rate of 10 sccm, maintains the pressure in a processing chamber at 133 Pa, exerts power of 200 W and 13.56 MHz on the inert gas to produce the plasma, and exposes the surface of the workpiece to the plasma for 3 to 5 min for light plasma sputter processing. The plasma is produced by high-frequency discharge or microwave discharge.
In this method, which subjects the workpiece to plasma sputter processing using the plasma of the inert gas before taking out the workpiece from the processing chamber into the atmosphere, the following reactions take place when the workpiece is exposed to the plasma.
(1) The workpiece is heated and, consequently, the reactive gas adsorbed by and adhering to the surface of the workpiece is forced to separate from the workpiece by heat.
(2) The reactive gas adsorbed by and adhering to the surface of the workpiece is forced to separate from the workpiece by the impact applied thereto by the plasma.
(3) The material forming the workpiece is oxidized and the chemical resistance of the workpiece against the reactive gas is enhanced.
These reactions purge the surface of the workpiece of the reactive gas adhering thereto and hence the workpiece will not be corroded when taken out from the processing chamber into the atmosphere.
The method (b) heats the workpiece at a temperature that purges the surface of the workpiece of the reactive gas adhering thereto and, consequently, the workpiece will not be corroded when taken out from the processing chamber into the atmosphere. The method (b) heats the workpiece in an evacuated environment maintained at a vacuum on the order of 1 to 5xc3x9710xe2x88x924 Pa by a heating means, such as a heating device to purge the surface of the workpiece of the reactive gas, such as Cl2 gas, adhering thereto. Practically, it is preferable that the workpiece is heated at a temperature in the range of, for example, 150 to 250xc2x0 C. The workpiece may be heated in an environment of an inert gas, such as N2 gas, instead of in an evacuated environment for the same effect.
The method (c) coats the surface of the workpiece with a carbon film and hence the reactive gas is adsorbed by the carbon film. Therefore, portions of the material of the workpiece other than those irradiated with the charged particle beam do not react on the reactive gas, and the workpiece can perfectly be purged of the reactive gas by removing the carbon film by an oxygen plasma ashing process subsequent to the reactive gas process. The carbon film may be formed so as to cover regions in the surface of the workpiece other than those in which a pattern is formed. Practically, the thickness of the carbon film is several hundreds angstroms. It is desirable to form the carbon film in the least necessary thickness.
Although the carbon film can be formed by a sputtering process, it is practically preferable to form the carbon film by a plasma CVD process because a pattern forming system is suitable for the plasma CVD process. Although residual portions of the carbon film remaining on the workpiece after a pattern has been formed may be left unremoved if the purpose of application permits, usually, it is desirable to produce an oxygen plasma and to burn and evaporate the carbon film by exposing the workpiece to the oxygen plasma (oxygen plasma ashing). The reactive gas adhering to the carbon film is removed together with the carbon film from the workpiece.
The method (d), which irradiates the workpiece with a charged particle beam while oxygen gas is blown against the surface of the workpiece, and the method (e), which irradiates the workpiece with an oxygen beam, oxidize the surface of the workpiece by the agency of the oxygen gas and remove the reactive gas adhering to the surface of the workpiece by the impact given thereto by the charged particle beam. Therefore, the workpiece will not be corroded when taken out from the processing chamber into the atmosphere.